Please check the MSUK Blue Book rules regarding competition seats and expiry dates.
Their has been extensions to the seats expiry date.
If you are going to buy new seats make sure you have as much time as possible on the new seats.
This is identifiable by the FIA label and hologram that is usually situated on the Left hand side of the seat.
The old labelling systems actually gave the month of manufacturer so the life was five years from then.
The new labelling system just gives the year so a seat labelled in 2014 will require changing at the end of 2019. In essence you may get nearly six years from a seat!
It is also worth checking if the new seat manufacturer is willing to inspect and possibly grant an extension to the life of the seat.
Some do some don’t, it’s worth checking?